Recently, I needed to combine two Array objects in JavaScript. I wanted an easy-to-read approach that ran fast. This led me to comparing a variety of the Array functions available in JavaScript. I…

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The safest approach is to use the concat method of an Array object to merge two Arrays. If speed is critical, you may consider using the spread syntax and the Array object’s push method. The concat function is the de-facto standard for merging arrays in JavaScript.

How to Efficiently Merge Arrays in JavaScript

Coding Ways to Combine Arrays in JavaScript

Comparing the Performance of Merging Arrays

What about using spread how it most commonly is by spreading into an new declaration all at once like:
<code>array1 = [...array1, ...array2]</code>
Or using push without spreading into it with it’s apply method:
<code>array1.push.apply(array1,array2)</code>
In my tests (chrome only) the first one is quite slow despite being the most common pattern, while the second is consistently slightly faster than concat and been around almost as long.  another interesting alternative at least.  thanks for the writeup and analysis.